Proper of the Mass

Those parts of the Mass which vary with the day according to the feast celebrated. It consists of

the first four chants of the choir

introit

gradual (or tract)

Alleluia (or perhaps a sequence)

offertory

Communion

lessons

epistle

Gospel (sometimes added lessons from the Old Testament)

the prayers said by the celebrant

collect

Secret

postcommunion

There are often several of each to commemorate feasts coinciding with that being kept.